1. Field of the Invention
The present invention relates to an elastic wave filter device in which an elastic wave filter chip is mounted on a package substrate, and more specifically to an elastic wave filter device with a ladder circuit configuration and a duplexer including the elastic wave filter device.
2. Description of the Related Art
In the past, an elastic wave filter device having a ladder circuit configuration has been widely used as a band pass filter. For example, Japanese Unexamined Patent Application Publication No. 2010-109694 listed below discloses an elastic wave filter device used as a transmission filter of a duplexer in a cellular phone. This elastic wave filter device includes a plurality of series arm resonators and a plurality of parallel arm resonators. In Japanese Unexamined Patent Application Publication No. 2010-109694, a bridge inductance is connected in parallel with a part of the series arm resonators. Meanwhile, an inductance for widening the pass band is connected between the parallel arm resonators and a ground potential.
In the elastic wave filter device described in Japanese Unexamined Patent Application Publication No. 2010-109694, the attenuation in a specific frequency range other than the pass band is increased by the bridge inductance. Further, band widening is performed by the inductance connected between the parallel arm resonators and the ground potential.
The above-described bridge inductance and the inductance connected to the parallel arm resonators are formed by the use of coil-shaped conductor patterns. Further, relatively large coil-shaped conductors are required due to a relatively high inductance ratio. Therefore, the inductances are formed not in an elastic wave filter chip but in a package element or material, such as a package substrate, for example. Due to the need to form such relatively large coil conductors, however, there is an problem with an increase in size of a package of the elastic wave filter device.